1. Field of Endeavor
The present invention relates to the field of rotating electric machines, and more particularly to a turbogenerator.
2. Brief Description of the Related Art
Turbogenerators are known, for example from EP-A2-1 209 802. They include a rotor which is rotatably mounted around a rotor axis and concentrically enclosed by a stator. A direct current-fed rotor winding is accommodated in the rotor and is in electromagnetic interaction with an alternating-current stator winding in the stator. The rotors of the turbogenerators are produced from magnetizable ferritic steels. In most cases, these rotors are produced from a rough forging, which is created as a monobloc, by corresponding machining. It is also conceivable, however, in the case of large turbogenerators, to assemble the rotor from a plurality of rotor parts, as is described, for example, in publications CH-A-150 099 and DE-PS-567 854. The rotor can be divided along the axis into a central rotor body and shaft ends which adjoin the ends of the rotor body and with which the rotor is rotatably mounted in corresponding rotor bearings. The middle region of the rotor body is the (electromagnetically) active region of the rotor.
Also, in the case of built rotors or rotors which are assembled from a plurality of parts, the rotor, on account of the same material being used for all the rotor parts, has the same magnetic properties throughout, which then leads to unfavorable electromagnetic conditions in the region of the body end of the rotor body or in the region of the shrink fit of the rotor end caps which are arranged on the end of the rotor body, which electromagnetic conditions manifest themselves in increased eddy-current losses and in an increased temperature loading.